This invention is generally directed to processes for the preparation of photogenerating compositions useful in layered photoresponsive imaging members. More specifically, the present invention is directed to processes for the preparation of amorphous inorganic photogenerating thin films by a simple and economical solution method. In one embodiment of the present invention, the process comprises dissolving the inorganic photogenerating or photoconductive material, such as an arsenic selenium alloy, thereafter formulating a photogenerating layer therefrom by deposition, for example, on a suitable substrate, and subsequently heating the aforementioned device. Subsequently, a charge transport layer is deposited thereon by a solution process to enable a layered imaging member useful in electrophotographic imaging systems. In another embodiment of the present invention, the charge transport layer can be situated between the supporting substrate and the photogenerator or photoconductive layer.
The formation and development of electrostatic latent images on the imaging surfaces of photoconductive materials by electrostatic means is well known, one such method involving the formation of an electrostatic latent image on the surface of a photoreceptor. A photoreceptor can comprise a conductive substrate containing on its surface a layer of photoconductive insulating material, and in many instances there can be selected a thin barrier layer between the substrate and the photoconductive layer to prevent charge injection from the substrate into the photoconductive layer upon charging of its surface.
Numerous different photoconductive members for use in xerography are known including amorphous selenium and amorphous selenium alloys. There are also known photoreceptor materials comprised of other inorganic or organic materials wherein the charge carrier generation and charge carrier transport functions are accomplished by discrete contiguous layers. Additionally, photoreceptor materials are disclosed in the prior art, which include an overcoating layer of an electrically insulating polymeric material, and in conjunction with this overcoated type photoreceptor there have been proposed a number of imaging methods.
Recently, there have been developed other layered photoresponsive devices including those comprised of generating layers and transport layers as disclosed in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference. Examples of photogenerating layers disclosed in these patents include trigonal selenium and vanadyl phthalocyanine, while examples of the transport layer that may be employed are comprised of certain aryl amines. This member is utilized in an electrophotographic copying method by, for example, initially charging the member with an electrostatic charge of a first polarity and imagewise exposing to form an electrostatic latent image which can be subsequently developed to form a visible image. Prior to each succeeding imaging cycle, the imaging member can be charged with an electrostatic charge of a second opposite polarity. Photogenerating pigments disclosed in this patent are usually prepared by complex vacuum evaporation methods. Also, there is disclosed in U.S. Pat. Nos. 4,232,102 and 4,233,383 the use of sodium carbonate doped and barium carbonate doped photoresponsive imaging members containing trigonal selenium, which are usually prepared by vacuum evaporation methods. Other representative patents disclosing layered photoresponsive devices, and the preparation of photogenerating compositions by vacuum evaporation include U.S. Pat. Nos. 4,115,116; 4,047,949 and 4,081,274.
Furthermore, there is illustrated in U.S. Pat. No. 3,148,084 processes for the formulation of photoconductive films wherein as one of the steps thereof there is sprayed onto a substrate a solution containing a soluble compound of at least one of the elements from Group VIA, and a soluble salt selected from other Groups such as 1A. Examples include selenium and sulfur with soluble salts of cadmium, copper, arsenic, and the like, reference columns 5 and 6. In contrast with the invention of the present application, soluble salts are not selected thereby enabling amorphous components, rather than crystalline materials; and further a high temperature spraying step is avoided with the process of the present invention. Moreover, with the process of the U.S. Pat. No. 3,148,084, the resulting products will most likely be contaminated because of the presence of the salts selected for the processes disclosed, which contamination would adversely affect the electrical characteristics of any resulting layered photoconductive imaging member prepared. The U.S. Pat. No. 3,148,084 is also of interest in that it discloses several processes for the preparation of films including evaporation processes, reference columns 1 and 2. Also of interest are U.S. Pat. Nos. 4,115,115 which describes processes for the formation of a layer of trigonal selenium dispersed in a polymer matrix by forming a solution of dibenzoyl peroxide, an organo selenium compound which interacts therewith, and a matrix polymer, thereafter applying the solution to a substrate, and accomplishing the other steps as detailed in the Abstract of the Disclosure, for example; and U.S. Pat. No. 4,421,838 which discloses the preparation of selenium in an insulating polymer by the reduction of an inorganic compound in the presence of the polymer. Patents of background interest include U.S. Pat. Nos. 2,898,240; 4,050,935; 4,053,311 and 4,481,273.
Although processes for the preparation of photogenerating materials are known, there remains a need for new processes that are simple and economical. There is also a need for processes for the preparation of photogenerating or photoconductive compounds wherein complex evaporation methods are avoided. Furthermore, there is a need for solution processes wherein amorphous photoconductive components are obtained in high yields. There is also a need for processes wherein imaging members can be prepared in a simple manner by solution methods. Moreover, there is a need for the preparation of photogenerating pigments by solution processes wherein there is avoided the spraying of the solution onto heated substrates. Further, there is a need for the low temperature preparation of thin amorphous photogenerating layers by solution processes. Also, there is a need for processes which provide layered electrophotographic imaging devices free of contaminations which affect the electricals.